The invention relates to a system and a method for optically testing surfaces for defects contained therein.
Quality control plays an important role in the automatic fabrication of industrial parts, in particular of semiconductor products and, in particular, explained using the example of a semiconductor wafer. The surface of a wafer should be free from conchoidal fractures after a sawing process, and be free from particles, and linking units such as fuses should be intact. Devices or methods that can be integrated into the organization of the fabrication should be applied in the appropriate testing of the surface in order to detect defects.
Depending on the size of a test object, and depending on the required resolution, a manual visual inspection with the aid of obliquely incident light and of a test object that executes wobbling movements can, for example, take place between individual method steps in the fabrication. Furthermore, an automatic inspection can be performed with the aid of a line scan camera by scanning once over the entire object. The number of pixels in the line and the width of the image dictate the pixel resolution per line unit. This is typically 40 μm.
Automatic inspection in the case of a conventional scanning operation is also known. Here, the surface of the test object is scanned with the aid of a two-dimensionally resolving camera. Variations in the illumination permit resolutions at different levels. Inspection with the aid of laser scanning on the basis of different principles is a further method from the related art. In this case, the laser beam mostly scans the object, object and laser beam moving at high speed relative to one another.
The method from the related art that is most promising for the automatic inspection of wafer surfaces is automatic inspection with the aid of a two-dimensionally resolving camera. However, manual visual inspection also continues to be applied.